1. Field of the Invention
The present invention relates to a driver device of magnetic heads for use in a magnetic record and reproduction apparatus such as a video tape recorder (VTR) or the like.
2. Description of the Background
In FIG. 5, there is shown a rotary drum of an independent 4 head type for use in a conventional video tape recorder (VTR). A rotary drum 1 is rotated at a speed of 1800 r.p.m. in a direction shown by an arrow X, and a magnetic tape 2, a recording medium having a thickness of 19 .mu.m is wound around approximately half the rotary drum 1 and runs at a speed of 3.335 cm/sec in a direction indicated by an arrow y in the VHS system. The rotary drum 1 is provided with four rotary video heads 100a, 100b, 100c and 100d having an azimuth angle of +6.degree. or -6.degree. on its periphery. The two heads 100a and 100b having a track width of 58 .mu.m for covering a standard mode are correctly arranged in opposite positions on the rotary drum 1, and the two heads 100c and 100d having a track width of 19 .mu.m for covering a triple speed mode are arranged on the rotary drum 1 in the same manner as the heads 100a and 100b.
In FIGS. 6 and 7, there is shown another rotary drum of a combined 4 head type for use in a conventional VTR. In this case, as shown in FIG. 7, a head 300a having a track width of 58 .mu.m for standard mode record and reproduction and a head 300d having a track width of 19 .mu.m for triple speed mode record and reproduction are mounted on a head base 201 at a distance of 1 H, i.e., 370 .mu.m to constitute combined heads. Heads 300b and 300c constitute combined heads in the same manner as the heads 300a and 300d. Two pairs of combined heads 300a, 300d, 300b and 300c are arranged in opposite positions on a rotary drum 201 as shown in FIG. 6.
In the conventional rotary drum of the independent or combined 4 head type shown in FIG. 5 or 6, in the standard mode record and reproduction, heads 100a and 100b or 300a and 300b are operated, while the heads 100c and 100d or 300c and 300d are just idled in an inoperative state. In the triple speed mode record and reproduction, the heads 100c and 100d or 300c and 300d are operated, while the heads 100a and 100b or 300a and 300b are in the inoperative state. In the conventional rotary drum of the combined 4 head type, since the azimuth angle of the heads 300a and 300c is determined to an equal angle .+-.6.degree. and the azimuth angle of the heads 300b and 300d is determined to an equal angle -6.degree., in a still image reproduction, when the tape is stopped, the image can be reproduced by using the two heads 300a and 300c. That is, since one recorded video track is reproduced by the two heads having the same azimuth angle (+6.degree.) and different head widths (the head 300a=58 .mu.m and the head 300c=19 .mu.m), a clear still image can be readily reproduced without blurring. As a result, the rotary drum of the combined 4 head type is widely used for a public VTR.
In FIG. 4, there is shown a driver circuit for the video heads 300a, 300b, 300c and 300d shown in FIG. 6. A rotary transformer 315 includes four primary coils 315a, 315b, 315c and 315d and four secondary coils 315e, 315f, 315g and 315h corresponding to the respective primary coils 315a, 315b, 315c and 315d. The two video heads 300a and 300b for the standard mode are connected to the two primary coils 315a and 315b, respectively, while the two video heads 300c and 300d for the triple speed mode are connected to the two primary coils 315c and 315d, respectively. A pair of reproduction head amplifiers 309L and 309R corresponding to the respective video heads 300a and 300b are connected to one end of the secondary coils 315e and 315f, respectively. A record amplifier 312 is coupled to the other ends of the secondary coils 315e and 315f through a capacitor 316. A 2 H (2 hour) record video signal is applied to the record amplifier 312 in a 2 hour standard mode recording. A pair of reproduction head amplifiers 310L and 310R corresponding to the respective video heads 300c and 300d are connected to one end of the secondary coils 315g and 315h, respectively. Another record amplifier 313 is coupled to the other ends of the secondary coils 315g and 315h through another capacitor 317. A -6 H (6 hour) record video signal is applied to the record amplifier 313 in a 6 hour triple speed mode recording.
A pair of switches a1 and b1 are connected between the ends of the respective secondary coils 315e and 315f and ground, and a switch c1 is connected between the other ends of the secondary coils 315e and 315f and ground. A pair of switches a2 and b2 are connected between the end of the respective secondary coils 315g and 315h and ground, and a switch c2 is connected between the other ends of the secondary coils 315g and 315h and ground.
A switch d1 selects one output of the reproduction head amplifiers 309L and 309R, and a switch d2 selects one output of the reproduction head amplifiers 310L and 310R. A switch e1 selects one of 2 H and 6 H terminals connecting common terminals of the switches d1 and d2, that is, one output of the switches d1 and d2. A reproduction video signal is output from a common terminal of the switch e1.
Now, the operation of the driver circuit shown in FIG. 4 will be described in detail.
In the standard (2 hour or 2 H) mode recording, the switches a1 and b1 are closed and the switch c1 is open. The 2 H record video signal is recorded on a magnetic tape through the record amplifier 312, the rotary transformer 315 and the video head 300a or 300b. In the standard mode reproducing, the switches a1 and b1 are open and the switch c1 is closed. The switch d1 is turned over every field, and the switch e1 selects the 2 H terminal. The reproduction video signal picked up by the video head 300a or 300b is output through the rotary transformer 315, the reproduction head amplifier 309L or 309R and the switches d1 and e1.
On the other hand, in the triple speed (6 hour or 6 H) mode recording, the switches a2 and b2 are closed and the switch c2 is open. The 6 H record video signal is recorded on the magnetic tape through the record amplifier 313, the rotary transformer 315 and the video head 300c or 300d. In the triple speed mode reproducing, the switches a2 and b2 are open and the switch c2 is closed. The switch d2 is turned over every field, and the switch el selects the 6 H terminal. The reproduction video signal picked up by the video head 300c or 300d is output through the rotary transformer 315, the reproduction head amplifier 310L or 31OR and the switches d2 and el.
With the conventional magnetic heads for the magnetic record and reproduction and the driver device therefore, as described above, the tape running speed is changed depending on the standard and triple speed modes, and the track width is also changed depending on the standard and triple speed modes. Hence, the heads having the suitable different track widths are required for the standard and triple speed modes.
Further, as shown in FIGS. 5 and 6, taking note of the half periphery of the rotary drum on which the magnetic tape is loaded, when the head 100b or 300b for the standard mode is actuated, the unoperated head 100c or 300c for the triple speed mode contacts the magnetic tape. Since the head generally projects 40 .mu.m from the outer peripheral surface of the rotary drum, when the head contacts the magnetic tape, the head beats on the magnetic tape to give vibrations to the magnetic tape and to cause the vibrations in the directions of X-, Y- and Z-axes. The vibration in the tape running direction (X-axis) causes the signals on the magnetized magnetic tape to carry out a speed modulation which causes a strong jitter phenomenon and brings about jitters in the reproducted image.
Consequently, even through it is unavoidable that the operated head beats the magnetic tape, the unoperated head 100c or 300c beats the magnetic tape at a different portion to cause the vibrations, and as an inevitable result, the vibrations are transmitted to another head 200b or 300b via the magnetic tape.
In the conventional combined 4 head type, as shown in FIG. 7, since two heads are combined on one block, the beating by the adjacent head of one block largely affects the other head. Further, in order to uniformly and stably contact the magnetic tape to the gap portions ga and gd of the combined heads, a high accuracy of curvature of the tape sliding surfaces of the heads and head mounting positions on the rotary drum are required, which are difficult to accomplish. Hence, problems at the contact surface between the head and the magnetic tape constantly arise, and the surfaces of the combined heads are frequently stuffed and smudged compared with a single head.
Furthermore, as shown in FIG. 4, since the pairs of heads are each independently switched over depending on not only the standard and triple speed modes but also the record and reproduction modes, the structure of the drive circuit for the heads becomes complicated. Further, in the reproduction mode, since slight reproduction signals are transmitted through the rotary transformer 315 and various switching operations are carried out, it is difficult to remove the noise, and in order to improve the signal-to-noise ratio (S/N) of the reproduction signal, there are many limits imposed on the shielding and the ground point. Further, in the combined 4 head type, as shown in FIG. 7, accurate realization of the gap of 370 .mu.m between the combined heads as mounted brings about a manufacturing cost increase.